Form line following guidance system

ABSTRACT

A first form line is defined using two or more terrestrial locations. The first form line may be predefined or may be defined by user during a spraying operation. A second form line is then computed using positioning data obtained while following the first form line and a swathing offset corresponding to the width of a spray pattern. The second form line is updated according to one or more deviations from the computed path. The deviations may correspond to operator inputted corrections which allow for obstacle avoidance, etc. The updating generally occurs by following the second form line as defined by the positioning data and the swathing offset and then deviating from the second form line to accommodate one or more terrain features. New GPS data is collected during these steps of following and deviating from the second form line and new positions are computed from the new GPS data. Finally, the updated second form line is defined using the new positions computed from the new GPS data. A further form line may then be defined using the updated second form line information and the swathing offset. A form line following apparatus may include a vehicle fitted with a GPS receiver configured to receive GPS data and GPS correction information and to compute form line following information therefrom. The form line following apparatus may also include a display device configured to receive and display the form line following information.

FIELD OF THE INVENTION

The present invention relates to precision farming methodologies and, inparticular, such methodologies as employ global positioning system (GPS)technologies.

BACKGROUND

In modern agricultural industries, accuracy is essential. Accuraterecord keeping, automated mapping, and precision farming techniques haveall become crucial factors in the challenge to improve overall cropsyields and comply with the ever increasing number of environmentalregulations. The accurate application of herbicides, pesticides andfertilizers is an essential component of modern precision farmingmethodologies. Whether such applications are performed by aerial orterrestrial techniques, advanced tools that provide highly accuratenavigation and guidance information for operators have become arequirement.

The transfer of global positioning system (GPS) technologies to civilianindustry has greatly assisted in meeting the challenges presented bytoday's precision agricultural needs. Using GPS systems, accurate andhighly reliable satellite-based positioning information, which typicallyachieves less than one meter accuracy by utilizing differential GPSposition corrections transmitted from fixed base stations, is providedto operators, for example though moving map displays. Such informationallows for precise navigation and guidance. Systems utilizing GPStechnology have been used in the past to assist in the aerial andterrestrial application of fertilizers, herbicides and pesticides, etc.However, such systems have generally been limited in their capabilities.

For example, as shown in FIG. 1A, GPS guidance systems which allowoperators to follow essentially parallel line spraying routes across afield have been used. For given field, an operator in a sprayer rig 10may begin a spraying pattern along an initial line 12. At the end of thefield, or at some point prior to the end of the field, the operatorgenerally maneuvers the sprayer rig 10 onto a return path 14. The returnpath 14 is essentially parallel to the initial path 12 and is separatedfrom the initial path 12 by distance corresponding to the width of thespray pattern. An alternative spraying pattern is shown in FIG. 1B. Thisspraying pattern resembles a race track pattern and again providesessentially parallel line spraying patterns.

Spraying patterns such as those shown in FIGS. 1A and 1B are useful foraerial applications and for terrestrial applications involving rowcrops. However, such spraying patterns are not well suited forterrestrial spraying applications involving open field crops, forexample, wheat, barley, etc. Typically, such crops are grown overterrain of varying contours and often in fields which present obstaclesto straight line spraying patterns. What is needed, therefore, is aprecision farming guidance and/or control system for terrestrialspraying applications which may be used in an open field cropenvironment.

SUMMARY OF THE INVENTION

In one embodiment, the present invention provides a method of form linefollowing. A first form line is defined using two or more terrestriallocations. The first form line may be predefined or may be defined byuser during spraying operations. A second form line is then computedusing positioning data obtained while following the first form line anda swathing offset corresponding to the width of a spray pattern. Thesecond form line is updated according to one or more deviations from itscomputed path.

The deviations may correspond to operator inputted corrections whichallow for obstacle avoidance, etc. The updating generally occurs asusers follow the second form line as defined by the positioning data andthe swathing offset and then deviate from the second form line toaccommodate one or more terrain features. New GPS data is collectedduring these steps of following and deviating from the second form line(as computed) and new positions are computed from the new GPS data.Finally, the updated second form line is redefined using the newpositions computed from the new GPS data and a further form line maythen be defined using the updated second form line information and theswathing offset.

In an alternative embodiment, the present invention provides a form linefollowing apparatus which includes a vehicle fitted with a GPS receiverconfigured to receive GPS data and GPS correction information and tocompute position information therefrom. A processor configured toreceive the position information and to compute form line followinginformation therefrom is also provided. The processor may be part of theGPS receiver or it may be a separate unit. The processor is alsoconfigured to update the form line following information in response toform line deviation information. The form line deviation information maycome, for example, from operator inputted corrections to accommodatevarious terrain features. The form line following apparatus may alsoinclude a display device configured to receive and display the form linefollowing information. The display device may include a moving mapdisplay and/or a light bar display which allow an operator to follow acomputed form line path.

Other features and advantages of the present invention will berecognized upon review of the following detailed description whereinreference is made to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and notlimitation, in the figures of the accompanying drawings in which:

FIG. 1A and 1B illustrate spraying guidance patterns provided by GPSsystems of the prior art;

FIG. 2 illustrates a spraying rig operating in an open field cropenvironment in accordance with the present invention;

FIG. 3 further illustrates the spraying rig operating in the open fieldcrop environment in accordance with the present invention;

FIG. 4 illustrates a form line following apparatus according to oneembodiment of the present invention;

FIGS. 5 illustrate a form line following process in accordance with oneembodiment of the present invention;

FIG. 6 illustrates the process of computing new form lines whendeviations from a projected form line path of at least a specifieddistance are recognized;

FIG. 7 illustrates various data layers in a geographic informationstructure;

FIG. 8A illustrates spraying operations on sloping terrain and theappropriate corrections required therefore according to one embodimentof the present invention;

FIG. 8B illustrates an alternative embodiment of the present inventionfor use on sloping terrain; and

FIG. 9 illustrates an alternative method of sprayer rig operations toaccount for obstacle avoidance in accordance with a further embodimentof the present invention.

DETAILED DESCRIPTION

A form line following guidance system is described. The system may findapplication in crop spraying operations or in other situations (e.g.,harvesting, ploughing, planting, mining, mineral prospecting, or otherapplications) where real-time correction information must be applied topreviously computed guidance paths. In one embodiment, a method of formline following includes defining a first form line using two or moreterrestrial locations. A second form line is defined using thepositioning data and a swathing offset. In general, the swathing offsetcorresponds to the width of a spraying pattern (i.e., a boom width). Inother cases, the swathing offset takes into account varying elevationswhich may be encountered, for example, when applying fertilizers, etc.over a field which includes a hillside or other sloping terrain. Thesecond form line is followed and updated according to one or moredeviations. The deviations may correspond to user inputted correctionsto accommodate one or more terrain features encountered during thespraying operations. GPS data may be collected during the steps offollowing and deviating from the computed second form line path and oneor more positions computed therefrom. An updated second form line maythan be defined using the computed positions.

In an alternative embodiment, a form line following apparatus includes avehicle fitted with a GPS receiver configured to receive GPS data andGPS correction information and to compute position informationtherefrom. A processor (which may be part of the GPS receiver or aseparate unit) is configured to receive the position information and tocompute form line following information therefrom and is furtherconfigured to update the form line following information in response toform line deviation information. Although the present invention isdescribed with reference to these and other exemplary embodiments, uponreview of this detailed description and the accompanying illustrationsit will be apparent to those skilled in the art that the presentinvention is equally applicable for use in a variety of other guidancesystems which accept operator inputted real-time corrections.Accordingly, the embodiments described below should be regarded asillustrative only.

Although the methods and apparatus of the present invention will bedescribed with reference to GPS satellites, it will be appreciated thatthe teachings are equally applicable to systems which utilizepseudolites or a combination of satellites and pseudolites. Pseudolitesare ground based transmitters which broadcast a PRN code (similar to aGPS signal) modulated on an L-band (or other frequency) carrier signal,generally synchronized with GPS time. Each transmitter may be assigned aunique PRN code so as to permit identification by a remote receiver.Pseudolites are useful in situations where GPS signals from an orbitingsatellite might be unavailable, such as tunnels, mines, buildings orother enclosed areas. The term "satellite", as used herein, is intendedto include pseudolites or equivalents of pseudolites, and the term GPSsignals, as used herein, is intended to include GPS-like signals frompseudolites or equivalents of pseudolites.

It will be further appreciated that the methods and apparatus of thepresent invention are equally applicable for use with the GLONASS andother satellite-based positioning systems. The GLONASS system differsfrom the GPS system in that the emissions from different satellites aredifferentiated from one another by utilizing slightly different carrierfrequencies, rather than utilizing different pseudorandom codes. As usedherein and in the claims which follow, the term GPS should be read asindicating the United States Global Positioning System as well as theGLONASS system and other satellite- and/or pseudolite-based positioningsystems.

In addition, the form line following guidance system described hereinmay be supplemented with non-satellite based guidance systems andmethodologies, such as inertial navigation systems, distance and gyrocompass and/or other heading indicator systems, laser range finding andbearing indicator systems, etc. The use of such systems to assist interrestrial navigation is well known in the art and will not bedescribed further so as not to unnecessarily obscure the presentinvention. It should be recognized that such systems could supplementthe GPS-based system described in detail below and would be particularlyuseful, for example, in situations where satellite-based positioningsignals are unavailable (e.g., under foliage, behind hills or buildings,in valleys, mines, etc.).

FIG. 2 illustrates a sprayer rig 30 operating in an agricultural field(or other plot of land) 32. Sprayer (or floater) rig 30 is equipped witha boom 34 which allows delivery of a variety of crop protectionproducts, conventional chemicals and/or liquid fertilizers. Examples ofthe crop protection products may include herbicides, pesticides, etc.The crop protection products or other chemicals or fertilizers aregenerally stored in a tank assembly 36 and are delivered through nozzles38 which are present in boom assembly 34. Various controls in the cab ofsprayer rig 30 allow an operator to control the flow of chemicals intank assembly 36 through boom 34 and nozzles 38, thus allowing theoperator to apply such chemicals where needed.

Field 32 may be any one of a number of growing fields. Preferably, field32 is an open field, i.e., not one configured for row crops. As such,field 32 may include growing crops such as wheat, barley, etc. As shown,field 32 has various contours and may be defined by irregular boundarylines.

Field 32 also includes a number of terrain features or obstacles such asrocks or boulders 40 and trees 42. Other obstacles such as ponds,streams, buildings, roads, etc. (not shown) may also be present. Duringspraying operations, sprayer rig 30 must avoid these obstacles and yetstill deliver the crop protection products and/or other chemicals whereneeded. To accomplish this task, sprayer rig 30 is fitted with a GPSantenna 44 which receives GPS data from one or more GPS satellites 46.Sprayer rig 30 will also include a GPS receiver capable of interpretingthe GPS data received through antenna 44 so as to provide guidanceinformation. The guidance system employed by sprayer rig 30 is unlikethe guidance systems of the prior art because, as those skilled in theart will appreciate, the parallel line guidance patterns available fromthe guidance systems of the prior art are unsuitable for use in field 32where obstacles such as rocks 40 and trees 42 prevent sprayer rig 30from following precise parallel line swathing (or spraying) patterns.

FIG. 3 illustrates an overhead view of field 32. Sprayer rig 30 is shownin proximity to a rock 40 within field 32. As shown by the guidance pathinformation presented as guidance path 50, sprayer rig 30 must follow aspraying path through field 32 which accommodates not only the contoursof the field but also the various terrain features and obstaclespresented therein. For example, sprayer rig 30 must avoid the rocks 40and trees 42 and yet still follow a path 50 which allows for preciseapplication of the various chemicals through boom assembly 34. Thevarious form lines 52, 54, 56, etc. of guidance path 50 are separated byapproximately the effective spraying width of boom assembly 34. Theoffset is sometimes referred to as a swathing offset and ensures thatall areas of field 32 are adequately (but not overly) covered by thespraying assembly as the chemicals are being applied.

Notice that guidance path 50 will be such as to accommodate operatorinputted corrections for deviations around obstacles such as rocks 40and trees 42. That is, after the first form line 52 is traversed bysprayer rig 30, a return path (form line 54) is computed which allowsfor an offset by approximately the width boom assembly 34. However, atvarious points along form line 54, operator inputted corrections, suchas those required to deviate around rock 40, will be input (e.g.,through a steering wheel). Thus, when computing the next form line (formline 56), these operator inputted deviations must be accounted for. Themanner in which this is accomplished by the present invention isdescribed below.

FIG. 4 illustrates the basic features of a form line following apparatusaccording to one embodiment of the present invention. FIG. 4 is drawnfrom the stand point of an operator console within sprayer rig 30.However, it will be appreciated that other embodiments with varyingconfigurations may also be used.

The form line following apparatus includes a GPS antenna 44 which ismounted on sprayer rig 30 so as to have a clear view of the sky. Thiswill ensure that antenna 44 is capable of capturing signals from GPSsatellites 46. Signals from antenna 44 are provided to GPS receiver 60which may be mounted inside the cab of sprayer rig 30 or at anotherconvenient location on the vehicle. Receiver 60 may also receivedifferential GPS correction information through antenna 48 from one of avariety of sources. For example, such differential GPS (DGPS) correctioninformation may be provided by radio telemetry from a GPS base stationsituated near field 32 as is common in the GPS arts. Alternatively, GPSreceiver 60 may receive differential GPS correction information from FMsubcarrier broadcasts or from other sources (e.g., satellitetransmissions as are currently available from the John Chance Co. in theUS or Racal in the UK). GPS receiver 60 uses the GPS data providedthrough antenna 44 from the GPS satellites 46 and the differential GPSinformation received through antenna 48 to compute position informationfor sprayer rig 30. The position information corresponds to theterrestrial location of sprayer rig 30 at the time the GPS data iscollected. Such position computations may occur periodically, forexample, several times each second. Using differential GPS correctiontechniques common in the art, submeter position accuracy may beobtained. In an alternative embodiment, GPS receiver 60 may beconfigured to operate with real-time kinematic (RTK) corrections whichprovide centimeter level accuracy. In general, however, submeteraccuracy is sufficient for most precision farming applications.

The position information computed by GPS receiver 60 is processed andprovided to display device 62. Display device 62 may include a movingmap display 64 which allows an operator to determine the preciselocation of sprayer rig 30 with respect to the boundaries of field 32.As illustrated, field 32 has some irregular boundaries and theintersection of cross-hairs 66 and 68 define the position of sprayer rig30 within field 32. The process for generating such moving map displayinformation is well known in the art and need not be described further.Also included on display device 62 may be a compass rose or headingindicator 70. Heading indicator 70 generally indicates the directionthat sprayer rig 30 is traveling. Through the use of moving map display64 and heading indicator 70, an operator is provided with simple andeffective information to control spraying operations within field 32.

Also included as part of the form line following apparatus is amulti-function light bar 72. The multi-function light bar 72 receivesguidance information from GPS receiver 60 and provides clear andimmediate guidance information/commands to an operator of sprayer rig 30through a row of light emitting diodes (LEDs). These LEDs are used toalert an operator when sprayer rig 30 has deviated from a computed formline path. The sensitively of light bar 72 (i.e., the deviation requiredbefore an LED will be illuminated to indicate that sprayer rig 30 isstraying from the computed path) may be operator configured for varioustypes of spraying operations and field conditions. In addition, thelight bar 72 may have a text screen (not shown) to display user selectedinformation such as the form line number, sprayer rig speed, flow rate,etc. In other embodiments, multi-function light bar 72 may be replacedby a liquid crystal or other display device configured to providesimilar course guidance and/or correction information.

During spraying operations, LED 74 will be lit when sprayer rig 30 isfollowing a computed form line path as described below. As sprayer rig30 deviates from the computed form line path, offset indicator LEDs 76,78, etc. will be lit to indicate the degree (or distance) of deviationfrom the computed path. Note that LEDs 76, 78, etc. will be lit ifsprayer rig 30 deviates to the right of the computed path andcorresponding LEDs on the other side of LED 74 will be lit if sprayerrig 30 deviates to the left of the computed path. Alternatively, LEDs76, 78, etc. may be lit to indicate that sprayer rig 30 should besteered to the right to get back to a computed form line path, etc. Thetimes at which the LEDs will be lit may be user configured. For example,LED 76 may be lit when sprayer rig 30 has deviated by two to three feetfrom the computed form line. Then, if sprayer rig 30 continues todeviate, for example to five feet from the computed form line path, LED78 may be lit. In other situations, LED 76 may not be lit until a fivefoot deviation has been recognized. In this way, the user is providedwith information which allows him or her to correct the path of sprayerrig 30 back to that of the computed form line.

Operator corrections and steering controls are input through steeringwheel 80. The form line following apparatus may be included with asteering input option which allows steering commands to be transmittedfrom a steering apparatus 82 to GPS receiver 60. Steering apparatus 82provides information regarding the steering inputs through steeringwheel 80 so that GPS receiver 60 can be provided with real-time updateinformation (e.g., the above-described deviations). Using the varioussteering commands provided through steering input apparatus 82, GPSreceiver 60 can provide appropriate display information to displaydevice 62 and light bar 72. In other embodiments, other heading sensorssuch as a gyro compass or flux-gate gyro compass may provide the updateinformation to GPS receiver 60. For the case where no steeringinformation is used, the form line following apparatus may rely onupdated position information derived from GPS data received fromsatellites 46 to compute and provide the display information.

FIG. 5 illustrates a general computation scheme which may be utilized byGPS receiver 60 (or a separate processor) in accordance with the presentinvention. Form line following process 100 starts at step 102 when anoperator begins the first form line. From step 102 the process moves tostep 104 where an operator defines the first form line. This may be doneas sprayer rig 30 is driven across field 32 using the form linefollowing apparatus, including GPS receiver 60, to collect and storeposition information or by down loading a previously computed form linemap from another source. Such a map may be obtained from a geographicalinformation structure (GIS) which also contains information on otheraspects of field 32 as described further below. Alternatively, theinformation may be provided from a stored map, such as may be generatedby digitizing an aerial photograph of field 32. In general, however, theoperator will define the first form line by driving across field 32 (orat least over that portion of field 32 that is to be sprayed), e.g.,following a fence line, a crop boundary line or a natural contour in theland, at step 106. This process finishes at step 108 when the first formline path has been completed. During this process, GPS data is collectedat a variety of geographic locations at step 110. Then, at step 112, theGPS data collection ends when the first form line has been completed.

FIG. 3 illustrates the process of data collection during the definitionof the first form line in more detail. Notice that as sprayer rig 30 isdriven across field 32, the form line following apparatus is activatedand GPS data is collected at a number of points 200, 204, 206, 208, 210,etc. The distance between these GPS data collection points is variable,and will typically correspond to submeter distances. The GPS datacollected at each point is processed along with the differential GPSinformation (or RTK corrections) and a series of terrestrial positionsare computed. These positions (when linked together, e.g., by a straightor curved line approximation) will define the first form line--that is,the path followed by sprayer rig 30 as it maneuvered across field 32. Inthis way, GPS receiver 60, or a separate processor, computes a firstform line which corresponds to the actual path traveled by sprayer rig30.

Returning to FIG. 5, if additional form lines are to be sprayed, adecision made at step 114, GPS receiver 60 (or the separate processor)computes a new form line (or swath) to be followed, based on the GPSdata collected while sprayer rig 30 traversed across the first form linepath. An offset due to, for example, the effective spraying width ofboom assembly 34 is also taken into account so that portions of field 32are not sprayed a second time. The computed new form line may be used togenerate guidance information for the operator of sprayer rig 30. Forexample, as the operator turns sprayer rig 30 around to follow a returnpath across field 32, the actual position of sprayer rig 30 (asdetermined by new GPS position information received by GPS receiver 60)is compared with its expected position (i.e., the second form lineinformation computed as described above). If the actual position agreeswith the expected position, the operator is so advised, e.g., by theillumination of LED 74 in light bar 72. This continues as sprayer rig 30is driven back across field 32 with new GPS data being constantlycollected and the actual position of sprayer rig 30 being constantlychecked against its expected position. As deviations from the expectedpositions are noted, display information is provided to the operator toallow guidance corrections as discussed above.

This process is further illustrated in FIG. 5 where, at step 118, theoperator begins the next form line. In general, the operator follows theguidance information computed by GPS receiver 60 and displayed on movingmap display 64 and heading indicator 70 and also on light bar 72. Duringthis time, the operator may input corrections for obstacle avoidance orterrain features using steering wheel 80 or another steering control.Ultimately, the operator will finish the second form line at step 122.

During the process of following the guidance information provided by GPSreceiver 60, new GPS data is collected at step 124. The new GPS datawill be used to provide guidance information as described above and willalso form the basis for computing any subsequent form line as was thecase where the GPS data collected while following first form line wasused to compute the second form line. GPS data collection for the secondform line ends at step 126. Notice that the subsequent form line iscomputed based on the actual path traveled by sprayer rig 30 and notjust the expected path computed after the first form line was completed.Thus, any deviations of sprayer rig 30 from the computed second formline, which were required due to the presence of rocks, trees, etc.,will be reflected in the new GPS data and the subsequent form line willtake into account these corrections.

If a subsequent form line is to be sprayed, a decision made at step 128,guidance information for that form line is computed at step 130, withoffset information being applied as before. These processes continueuntil the spraying operations for field 32 are completed at step 132 atwhich time the form line following process 100 quits at step 134. Noticethat a decision process at step 132 allows an operator to indicate thata current set of form lines have been completed but that the completeset of operations for the field have not been completed. This situationmay arise, for example, where different crops are situated in the samefield or where a new chemical is being applied. In such cases, theoperator may indicate that a new set of form lines (corresponding to thenew conditions) should be initiated, beginning at step 102.

In some cases, form line following process 100 may be configured so thatonly deviations greater than a specified distance from an intended trackare recognized. That is, only significant deviations from a computedform line guidance path (e.g., the second form line discussed above)will be used as decision points for displaying guidance correctioninformation to the user. To illustrate, consider the situationillustrated in FIG. 6. As shown, a sprayer rig operating in a field 150was supplied with guidance information (e.g., using the above describedform line following process 100 ) that would have the sprayer rig followan intended path 152. However, while traversing field 150, the sprayerrig actually followed a path 154. Path 154 is somewhat different thanthe intended path 152 and includes a deviation 156 around obstacle 158.

It will be appreciated that, in accordance with form line followingprocess 100, GPS data is collected while the sprayer rig is traversingpath 154. Therefore, GPS receiver 60 may perform numerous computationsthat indicate that the sprayer rig is not following the intended formline path 152. However, where these deviations are not significant, itwould be burdensome, both in terms of computation operations and interms of operator fatigue, to constantly display guidance correctioninformation to the user. In other words, if guidance correctioninformation (e.g., illumination of various LEDs of light bar 72) wereconstantly displayed to the user even when the deviations of the sprayerrig from a intended path were not significant, a user would soon growweary of constantly having to steer the sprayer rig left and right tocorrect these minor deviations.

Accordingly, form line following process 100 may be configured so thatdeviations which are not significant are "ignored". That is, when GPSreceiver 60 recognizes that the sprayer rig has only deviated from theintended form line path by a distance less than a specified distance, nonew guidance information is displayed (e.g., LED 74 will be lit as ifthe sprayer rig was still on the intended path). Then, when asignificant deviation, such as deviation 156, is recognized, appropriateguidance information which will allow the operator to regain theintended path will be displayed.

As illustrated in FIG. 6, the predefined distance which will trigger thedisplay of guidance information essentially "broadens" the width of theintended form line path 152 to a "lane". The lane width may be userconfigurable and will typically correspond to a few feet, depending onfield conditions. As significant deviations are recognized, appropriateguidance information is displayed. The guidance information may bedisplayed before the operator veers outside of a lane so that excessive"zig-zagging" will be avoided. Thus, the risk of producing cumulativeerrors over several form lines is reduced and the intended paths of thesprayer rig through the field remain relatively straight. These factorsall contribute towards reducing the operator's steering burden andoperator fatigue.

Notice also in FIG. 6 that the next intended form line 160 is computedbased on the actual path 156 traversed by the sprayer rig. Thus, thedeviation around obstacle 158 is accounted for. Likewise, the thirdintended form line path 162 will be computed based on the actual path164 driven by the sprayer rig.

As indicated above, form line following information may also be providedby an external source. FIG. 7 shows illustrative data layers which maybe provided in a geographic information system (GIS). A GIS is a systemof hardware, software and geographic data designed to support thecapture, management, manipulation, analysis, modeling and display ofspatially referenced data for solving complex planning and managementproblems. The main propose of a GIS can be to find solutions to problemsby using both geographic and tabular data. For the example shown, GIS200 (which may exist inside a computer system) includes informationrelating to various soils, ownership (e.g., fence lines), roads,streams, elevation, fields, and other data, all of which may be overlaidon a base map of field 32. The spraying information provided by GPSreceiver 60 in the course of computing various form lines may also beprovided as a layer in GIS 200. In this way, a user will haveinformation regarding the application of the various chemicals at pointsof interest on field 32. This may assist a farmer in various precisionagricultural operations by comparing which spray formulas achievedbetter crop yields. Alternatively, the form line information fromprevious spraying operations may be downloaded for use in new sprayingoperations by providing guidance information as described above.

Up to this point it has been assumed that the field in which the sprayerrig operates is relatively flat. However, in those situations where thesprayer rig will operate over sloping terrain, certain corrections mustbe accounted for. In particular, it will be appreciated that when thesprayer rig is operating on a hillside or other sloping terrain, theboom assembly 34 will have an effectively shorter horizontal spraying(or swath) width than it would have when the sprayer rig operates onessentially flat terrain. Indeed, the effective horizontal sprayingwidth of the boom assembly 34 may be approximately equal to the physicallength of the boom assembly multiplied by the cosine of the angle of theslope of the terrain (assuming the spraying nozzles do not directchemicals significantly beyond the ends of the boom assembly 34). Thatis,

    effective horizontal swath width=physical swath width·cos .O slashed., where .O slashed.=slope of the terrain.

This situation is illustrated in FIG. 8A which shows a first form linepath 250 over a hillside 252. During spraying operations, a sprayer rigtraveled along the first form line 250 and reached a position 254defined by coordinates x₁, y₁, z₁. Now on the return path, the sprayerrig needs to be guided to a position 256 which is offset from position254 by the effective spraying swath distance. Position 256 is defined bycoordinates x₂, y₂, z₂ and, assuming that y₁ ≈y₂, then ##EQU1##

GPS receiver 60 will have computed x₁ and z₁ while the sprayer rig wastraveling along form line 250. Further, positions x₂ and Z₂ will becomputed from GPS data received while the sprayer rig is traveling alongthe second form line 260. It will be appreciated that by the time thesprayer rig reaches position 256 and computes x₂ and z₂, the sprayer rigwill have already passed position 256. Thus, the guidance informationwill be late. However, because GPS receiver 60 computes new positioningdata several times each second, the distance traveled by the sprayer rigwill be insignificant. In addition, guidance smoothing and predictivefilters (e.g., Kalman filters) can be employed to reduce the effects ofthis lag time between the receipt of new GPS data and the calculation ofguidance information.

In alternative embodiments, such as that illustrated in FIG. 8B, sprayerrig 30 may be equipped with GPS antennas 44 at either end of boomassembly 34. This would allow GPS receiver 60 to compute the elevationsof each end of the boom assembly 34 (provided DGPS or RTK correctionsare used) and thereby derive the slope of the terrain (i.e., the angle.O slashed.). This information could then be used to compute theeffective horizontal swath width as described above, eliminating theneed for guidance and predictive filters as may be required in a singleantenna situation. This concept may be expanded to equip sprayer rig 30with three antennas, two on boom assembly 34 and one positioned (forexample) on the cab, to allow the computation of three elevationparameters. This may be useful for undulating terrain where not onlyhorizontal slope (i.e., roll), but also longitudinal slope (i.e., pitch)must be accounted for.

A further embodiment may equip sprayer rig 30 as described in U.S. Pat.No. 5,268,695 to Dentinger et al. (the "'695 patent"), assigned to theAssignee of the present invention. The '695 patent describes methods andapparatus for differential phase measurement through antennamultiplexing and the entire disclosure is incorporated herein byreference. In one embodiment, multiple GPS antennas are connected to aGPS receiver so that a carrier signal received by the antennas is timemultiplexed through a single hardware path to the receiver where areference oscillator is used to compare the phase of the signal fromeach antenna to the phase of a reference signal. One of the antennas isdesignated as the reference antenna and the carrier signal received bythe reference antenna is used to phase lock the reference signalgenerated by the reference oscillator. The phase of the same carriersignal received by the other antennas is periodically compared to thephase of the reference signal and each comparison results in a singlephase angle measurement for the respective antennas compared to thereference antenna. The computed phase angle measurements allow for thecalculation of the angle of inclination of a plane in which the multipleantennas are situated. Thus, using such a system, the angle ofinclination of the boom assembly 34 could be computed and, hence, theeffective horizontal swath distance derived.

An alternative to the form line following process 100 is illustrated inFIG. 9. Sprayer rig 300 is operating in a field and will proceed alongessentially parallel form lines 302, 310, etc. These form lines may beprecomputed and will not take into account operator-inputted deviations.To avoid over application of chemicals, however, the nozzles of boomassembly 304 will be controlled so that the obstacles (and the resultingdeviations of sprayer rig 300) are accounted for.

To illustrate, consider that as sprayer rig 300 travels along form line302, eight nozzles of boom assembly 304 are operating and, thus,chemicals are being applied over a swath path equal to the width of boomassembly 304 and centered on form line 302. As sprayer rig 300 maneuversaround obstacle 306, a form line following apparatus similar to thatdescribed above recognizes that portions of boom assembly 304 are nowpositioned over areas of the field to be sprayed when sprayer rig 300 istraveling along form line 310. That is, portions of boom assembly 304are encroaching on a swath path to be covered during another pass on adifferent form line. Accordingly, the form line following apparatus willshut off those nozzles which are positioned outside the swath pathassociated with form line 302 and, thus, this area will not be sprayedwith chemicals. Instead, the area will be sprayed when sprayer rig 300travels along form line 310.

This operation achieves the same result as form line following process100 and also accounts for the deviations around obstacle 306. Analternative approach would be to turn off the appropriate nozzles whensprayer rig 300 travels along form line 310 (assuming all nozzles wereoperating when the swath associated with form line 302 was beingsprayed). Other approaches utilizing collapsible boom assemblies 34 mayalso be used.

To accommodate a process such as that illustrated in FIG. 9, sprayer rig300 is fitted with a form line following apparatus similar to thatdescribed above and a nozzle control device is provided such that nozzlecontrol commands from GPS receiver 60 will control the application ofchemicals.

In addition to allowing a human operator to steer a spraying rig alongintended paths, the present invention may be adapted for use withsemi-autonomous or fully autonomous vehicles which provide some level ofrobotic control. Ground vehicles which make use of GPS technology toprovide navigation information are now being developed. For example,RAHCO International has developed a track mounted, unmanned groundvehicle for hazardous waste transport. A description of the vehicle andits navigation and obstacle avoidance system is provided in a paper byRaymond C. Daigh, entitled "High Reliability Navigation for AutonomousVehicles" delivered and published as part of the 1996 Trimble Surveying& Mapping User's Conference User Application Papers. This entiredisclosure is incorporated herein by reference. Briefly, the vehicleincorporates a dead reckoning system which includes a rate gyro, anelectronic compass and track encoders (the vehicle uses tracks insteadof wheels) along with a differential GPS positioning system. This systemallows for real time positioning and navigation at moderate speeds.Those skilled in the art will appreciate that systems employing moresophisticated RTK systems (which provide centimeter level accuracy andlow latency updates) may allow for operations at higher speeds.

In addition to the above-described navigation system, the vehicledeveloped by RAHCO International includes a collision avoidance system.The collision avoidance system includes an array of ultrasonic sensorsmounted on each end of the vehicle and arranged to provide overlappingcoverage. Although not discussed by Mr. Daigh, other sensors such asradar, laser range finding equipment and robotic vision systems couldalso be used for such a collision avoidance system.

Those skilled in the art will recognize, in light of the abovedisclosure, that a robotic vehicle such as that described by Mr. Daighcould be enhanced by incorporating a form line following system similarto the present invention. In general, such an autonomous vehicle wouldbe provided with a navigation and collision avoidance system such asthat developed by RAHCO International and would also include the formline following methods and apparatus of the present invention. Thevehicle navigation system would be provided with form line followinginformation as described above which, in conjunction with the inertialnavigation and DGPS equipment could be used to guide the vehicle in afield or other environment. Obstacles detected by the collisionavoidance system would be steered around (by the use of steering outputcommands provided by the steering avoidance system and new GPS datawould be collected during these deviations. This new GPS data would beused to compute updated form lines as described above and thisinformation could be provided as steering inputs to the vehicle'snavigation system. Of course, in some cases the features of a fullyautonomous vehicle could be combined with the guidance equipment (e.g.,a multi-function light bar) associated with human operator controlledequipment to provide a semi-autonomous vehicle.

Thus, a form line following guidance system has been described. Althoughdescribed with reference to specifically illustrated embodiments, thepresent invention has application to a variety of other guidance system.Accordingly, the present invention should be limited only by the claimswhich follow.

What is claimed is:
 1. A method of form line following, comprising thesteps of:defining a first form line using two or more terrestriallocations; defining a second form line using positioning data derivedfrom GPS data and a swathing offset; and updating said second form lineaccording to one or more deviations from said second form line byfollowing said second form line defined by said positioning data andsaid swathing offset, deviating from said second form line toaccommodate one or more terrain features, collecting new GPS data duringsaid steps of following and deviating and computing one or morepositions therefrom, and defining an updated second form line using saidpositions.
 2. A method as in claim 1 further comprising the step ofdefining a third form line using said positions and said swathingoffset.
 3. A form line following apparatus, comprisinga vehicle fittedwith a GPS receiver configured to receive GPS data and GPS correctioninformation and to compute position information therefrom; and aprocessor configured to define an updated form line according toposition information computed while the vehicle was (a) following apreviously computed form line having been defined using positioning dataderived from earlier received GPS data and a swathing offset, and (b)deviating from the previously computed form line to accommodate one ormore terrain features.
 4. A form line following apparatus as in claim 3further comprising a display device configured to receive and displayform line following information corresponding to the updated form line.5. A form line following apparatus as in claim 4 wherein said vehicle isfurther configured with an automatic steering apparatus configured toaccept steering inputs according to said form line following informationand to provide steering outputs to control said vehicle in accordancetherewith.
 6. A method of form line following, comprisingcontrolling avehicle so as to follow a form line computed using positioninginformation provided by one or more sources of GPS information while thevehicle was (a) following a previously computed form line having beendefined using earlier positioning information and a swathing offset, and(b) deviating from the previously computed form line to accommodate oneor more terrain features encountered while following the previouslycomputed form line.
 7. A method as in claim 6 wherein said positioninginformation is provided by one or more GPS satellites.
 8. A method as inclaim 6 wherein said positioning information is provided by one or morepseudolites.
 9. A method as in claim 6 wherein said positioninginformation is provided by a GPS receiver housed within said vehicle.10. A method as in claim 6 wherein said positioning information isprovided by a GPS receiver located remote from said vehicle.
 11. Amethod comprisingoperating a spraying apparatus along a form line so asto apply chemicals to a portion of a field, the form line having beendefined according to positions computed while (a) following a previouslycomputed form line having been defined using previously derivedpositioning information and a swathing offset, and (b) making deviationsfrom the previously computed form line to account for one or moreterrain features encountered while operating said spraying apparatusalong the previously computed form line.
 12. A method as in claim 11wherein the deviations are accounted for by applying chemicals only to aselected area of the field while operating along the form line, theselected area configured so as not to encroach upon other portions ofthe field upon which chemicals were applied while operating the sprayingapparatus along the previously computed form line.